If a person (or an animal) is cross-eyed, both eyes turn in towards the nose instead of looking straight ahead together. The two eyes are not aiming at the same spot. Some people are born this way; sometimes it is only slight, and glasses or an operation can help. Children may use the word in a teasing way, which is unkind — the eyes are just built that way. People also stretch it: “this page is making me go cross-eyed” means the print or the pattern is so busy that your eyes feel tired and will not settle. Though actually, do not mix this with British “squint.” In Britain, a squint often means the same problem with the eyes; in American English, to squint is usually just to narrow your eyes in bright light. And it is not “cross” as in a bit angry. The feeling and the eyes are different words that happen to look alike.